[libvirt] [PATCH 4/4] storageVolCreateXMLFrom: Check if backend knows how to createVol

[Erik Skultety]

On 10/02/16 17:28, Michal Privoznik wrote:
> It is highly unlikely that a backend will know how to create a
> volume from a different volume (buildVolFrom) and not know how to
> create an empty volume (createVol). But:
> 1) we call the function without any prior check so if that's the
> case we would SIGSEGV immediatelly
> 2) it's better to be safe than sorry.
> 
> Signed-off-by: Michal Privoznik <mprivozn at redhat.com>
> ---
>  src/storage/storage_driver.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/src/storage/storage_driver.c b/src/storage/storage_driver.c
> index e0ded01..81b1584 100644
> --- a/src/storage/storage_driver.c
> +++ b/src/storage/storage_driver.c
> @@ -2037,6 +2037,13 @@ storageVolCreateXMLFrom(virStoragePoolPtr obj,
>      if (newvol->target.capacity < origvol->target.capacity)
>          newvol->target.capacity = origvol->target.capacity;
>  
> +    if (!backend->createVol) {
> +        virReportError(VIR_ERR_NO_SUPPORT,
> +                       "%s", _("storage pool does not support volume "
> +                               "creation"));
> +        goto cleanup;
> +    }
> +
>      if (!backend->buildVolFrom) {
>          virReportError(VIR_ERR_NO_SUPPORT,
>                         "%s", _("storage pool does not support"
> 

Although I'm still not 100% convinced, how would one attempt to
implement volBuild which takes a freshly created volume in that pool
without actually supporting volume creation. And if one's aware of this,
in my mind, this would effectively end up a deadcode.
But the logic is correct and being a little paranoid never hurts, so
it's an ACK, unless someone would like to oppose, in which case, feel
free to speak.

Erik